The present invention relates to relief valves, and more particularly to such a relief valve which automatically pulls down an indicator with display face out of the shade of a cap when it is opened by an abnormal pressure. It won't affect the function of releasing abnormal pressure of the relief valves when the indicator was shown, and the indicator can be reset for the next warning.
A variety of apparatus including transformers, oil tanks, oil reservoirs, gas tanks, oil pipes, etc. may be equipped with a relief valve for releasing excessive pressure. If the inside pressure of an enclosed apparatus is continuously increased, the apparatus may be caused to explode. Regular relief valves for, this purpose do not produce any signal to notify the maintenance persons when they had been already actuated to release pressure. Therefore, maintenance presons cannot quickly find the reason when an excessive high pressure happens.